Fats are the basic components that have an important place in human and animal nutrition and give the highest energy per unit weight. It is the most important nutritional factor affecting the energy level and reproductive function of the feed. oils; Since they contain more energy than carbohydrates and proteins, they play an important role in the performance of animals. Many scientific studies reveal the importance of preserved oils (bypass oils) in animal nutrition. The addition of calcium salts of fatty acids to ruminant diets leads to an increase in plasma cholesterol and progesterone levels, which leads to an increase in ovulation rate and embryo quality (Spicer et al. 1993). Preserved fat additive is the most suitable among them, preserved fat does not cause rumen acidosis and does not adversely affect cellulose digestion in the rumen (Yilmaz et al., 2009). McNamara et al. (2003) reported that the addition of preserved fat improves fertility properties in their studies in which they examined the effects of adding fat to the ration of dairy cattle on reproductive performance. In cases where sufficient amount of fat is not added to the rations, problems may be experienced in meeting the energy needs of the animal, as well as in various reproductive functions. In order to eliminate these negative effects, preserved fat should be added to the ration. Newly born and/or high-performing dairy animals need much more than the energy they get from the feed they eat to produce milk. In order to meet these needs, they use the fat stores in their bodies. As a result, the animal weakens; appetite and milk yield decrease, the animal loses weight, fertility decreases, its metabolism deteriorates and ketosis cases occur. Bypass oils meet the energy needs of animals in regular use; It helps to keep in shape and increase the performance of meat, milk and progeny.